Although alcohol and substance use disorders (ASUDs) are common in HIV-infected patients, little is known about the efficacy and comparative effectiveness of ASUD treatments in HIV-infected populations. Further, because few individuals with ASUD receive high quality ASUD treatment of any type, understanding the factors associated with initiating, engaging, and remaining in ASUD treatment is at least as important as the specific type of treatment. Understanding issues of treatment initiation, engagement, and retention is critical to advancing comparative effectiveness research in ASUD, particularly as provisions of the Affordable Care Act (ACA) are implemented. We will use the Veterans Aging Cohort Study (VACS) to study the comparative effectiveness and delivery of ASUD treatment in HIV-infected Veterans. VACS is a large multisite, national study with 2 main components: 1) a Virtual Cohort of 44,180 HIV-infected Veterans and 88.360 uninfected comparators on which we have access to administrative, pharmacy, laboratory, pathology, health service utilization, and linked Medicaid/Medicare data; and 2) VACS 8, a prospective cohort of 3631 HIV-infected and 3693 matched HIV-uninfected Veterans that adds annual self-report survey information to data available in the Virtual Cohort. Our Specific Aims are to: 1) Compare the effectiveness of initiation, engagement, and retention in different types of ASUD treatment on quality of HIV care, virologic suppression, and costs in HIV-infected Veterans with ASUD; 2) Identify predictors of initiation, engagement, and retention in ASUD treatment in HIV- infected Veterans; and 3) Assess effects of ACA insurance expansion on initiation, engagement, and retention in ASUD treatment for HIV-infected Veterans. Aims 1 and 2 will use the VACS Virtual Cohort and Aim 3 will use the VACS 8 prospective cohort. For Aim 1, we will use a quasi-experimental, propensity-score adjusted, difference-in-differences analysis of outcomes before and after new ASUD treatment episodes in VACS Virtual Cohort participants. For Aim 2, we will conduct time-updated, generalized estimating equations logistic regression analyses to identify independent predisposing, enabling, and need predictors of initiation, engagement, and retention in ASUD treatment among HIV-infected VACS Virtual Cohort participants. For Aim 3, we will use a mixed-methods approach to prospectively assess HIV-infected VACS 8 participants with ASUD over several years as the ACA insurance expansion occurs. Achieving these aims will provide real world estimates of which ASUD strategies are associated with the best outcomes in a national sample of vulnerable HIV-infected patients and identify factors associated with increased engagement and retention in treatment.